Related Experiment Videos
Substrate specificity of age-related changes in the inducibility of hepatic microsomal monooxygenases in middle-aged
Abstract:
Hepatic microsomal monooxygenase induction was investigated in young-adult and middle-aged male Fischer 344 rats. Monooxygenase components and drug metabolism activities were determined in liver microsomes prepared from rats treated with phenobarbital (PB, beta-naphthoflavone (BNF) or methyltestosterone (MT) and compared with values from untreated rats. PB and BNF effects on cytochrome P-450 concentration and cytochrome c reductase activity were similar in young-adult and middle-aged animals. However, the extent of cytochrome P-450 induction by MT was less in the older animals. The age-related changes in induction of drug metabolism activities differed with different substrates for the monooxygenase system. In contrast to the inducibility of benzphetamine N-demethylation and aniline hydroxylation, which was diminished in the older rats, the inducibility of nitroanisole O-demethylation was enhanced. The results imply that qualitative changes in the microsomal enzyme system occurred as the animals progress from young to middle adulthood.
Insights
Drug metabolism in rats changes with age. While some liver enzyme activities remained similar, others like methyltestosterone induction decreased in older rats, showing age-related shifts in hepatic microsomal monooxygenase function.
Area of Science:
- Pharmacology
- Biochemistry
- Gerontology
Background:
- Hepatic microsomal monooxygenases are crucial for drug metabolism.
- Age can influence the activity and inducibility of these enzymes.
- Fischer 344 rats are a common model for aging studies.
Purpose of the Study:
- To investigate age-related changes in hepatic microsomal monooxygenase induction.
- To compare the effects of different inducers (phenobarbital, beta-naphthoflavone, methyltestosterone) on enzyme activity in young-adult and middle-aged rats.
- To determine if age affects specific drug metabolism pathways differently.
Main Methods:
- Liver microsomes were prepared from young-adult and middle-aged male Fischer 344 rats.
- Rats were treated with phenobarbital (PB), beta-naphthoflavone (BNF), or methyltestosterone (MT).
- Monooxygenase components (cytochrome P-450, cytochrome c reductase) and drug metabolism activities were measured.
Main Results:
- PB and BNF induced cytochrome P-450 and cytochrome c reductase similarly in both age groups.
- Methyltestosterone (MT) induction of cytochrome P-450 was lower in middle-aged rats compared to young-adults.
- Age-related differences were observed in substrate-specific metabolism: benzphetamine N-demethylation and aniline hydroxylation decreased, while nitroanisole O-demethylation increased in older rats.
Conclusions:
- Hepatic microsomal enzyme systems undergo qualitative changes with age.
- The inducibility of drug metabolism pathways is differentially affected by aging.
- These findings highlight age-dependent alterations in the liver's capacity to metabolize xenobiotics.